Method and apparatus for electrochemical-mechanical planarization

ABSTRACT

A method for performing electrochemical-mechanical planarization (EMP) of a workpiece surface including a pattern of electrical conductors comprises supplying a chemical-mechanical polishing (CMP)-type apparatus having an abrasive or non-abrasive polishing pad with an oxidizer-free, electrolytically conductive, abrasive or non-abrasive fluid and applying a time-varying anodic potential to the workpiece surface for controllably dissolving the material, e.g., metal, of the electrical conductors while simultaneously applying mechanical polishing action to the surface. The method advantageously reduces or substantially eliminates undesirable dishing characteristic of conventional CMP planarization processing utilizing chemical oxidizer agent(s). Apparatus for performing EMP are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of copending application Ser. No.09/450,937 filed on Nov. 29, 1999.

FIELD OF THE INVENTION

[0002] The present invention relates to a method and apparatus forelectrochemically-assisted or -augmented mechanical planarization, i.e.,electrochemical-mechanical planarization (“EMP”), which method andapparatus enjoy particular utility in the manufacture of semiconductorintegrated circuit devices.

BACKGROUND OF THE INVENTION

[0003] Chemical-mechanical polishing (CMP) techniques and apparatustherefor have been developed for providing smooth topographies,particularly on the surfaces of layers deposited on semiconductorsubstrates during integrated circuit manufacture. In such instances,rough topography results when metal conductor lines are formed over asubstrate containing device circuitry, e.g., inter-level metallizationpatterns comprising a plurality of electrically conductive lines whichmay, inter alia, serve to interconnect discrete devices formed withinthe substrate. The metal conductor lines are insulated from each otherand from vertically adjacent interconnection levels by thin layers ofdielectric insulation material, and openings formed through theinsulating layers provide electrical interconnection and access betweensuccessive such interconnection levels. In fabricating such type devicesincluding multiple interconnection and insulative layers, it isdesirable that the metallic and insulative layers have a smoothtopography, inasmuch as it is very difficult to photolithographicallyimage and pattern layers applied to rough surfaces. CMP can also beemployed for removing different layers of material from the surface of asemiconductor substrate, as for example, following via hole formation inan insulating layer, when a metallization layer is deposited and thenCMP is used to form planar metal via plugs embedded in the insulatinglayer.

[0004] Briefly, CMP processes utilized in semiconductor devicemanufacture involve mounting a thin flat workpiece, e.g., asemiconductor wafer substrate, on a carrier or polishing head, with thesurface to be polished being exposed. The substrate surface is thenurged against a wetted polishing surface, i.e., a rotating polishingpad, under controlled mechanical pressure, chemical, and temperatureconditions. In addition, the carrier head may rotate to provideadditional motion between the substrate and polishing pad surfaces. Apolishing slurry containing a polishing agent, such as alumina (Al₂O₃)or silica (SiO₂) finely-dimensioned particles is used as the abrasivematerial. Additionally, the polishing slurry contains a number ofchemicals, including pH adjusting and stabilizing agents, as well aschemical oxidizing agents for chemically removing (i.e., etching)various components of the surface being planarized. The combination ofmechanical and chemical removal of surface material during the polishingprocess results in superior planarization of the polished surface,vis-à-vis other planarization techniques.

[0005] Slurries used for CMP can be divided into three categories,depending upon their intended use: silicon (Si) polish slurries, oxidepolish slurries, and metal polish slurries. Si polish slurries aredesigned to polish and planarize bare Si wafers and are typicallycomposed of very small (i.e., about 20-200 nm diameter) abrasiveparticles, e.g., of silica (SiO₂), alumina (Al₂O₃), or ceria (CeO₂),suspended in a water-based liquid at a somewhat basic pH provided by apH adjusting agent, typically a hydroxide-type base. Oxide polishslurries are designed to polish and planarize a dielectric layer on awafer, typically a layer of silicon dioxide (SiO₂), and are similarlycomposed of very small abrasive particles (i.e., about 20-1000 nmdiameter) of, e.g., SiO₂, Al₂O₃, or CeO₂, suspended in a water-basedliquid at a high (i.e., basic) pH.

[0006] Metals polish slurries are designed to polish and planarizeconductive layers on semiconductor wafer substrates. The conductivelayers are typically deposited on a dielectric layer and typicallycomprise metals such as tungsten (W), titanium (Ti), aluminum (Al),copper (Cu), alloys thereof, semiconductors such as doped silicon (Si),doped polysilicon, and refractory metal silicides. The dielectric layertypically contains openings (“vias”) that are filled with the conductivematerial to provide a path through the dielectric layer to previouslydeposited layers. After the conductive layer is polished, only theconductive material filling the vias remains in the dielectric layer.

[0007] Metal polish slurries utilized for such CMP of vias typicallyinclude very small particles (i.e., about 20-1000 nm diameter) of theabove-mentioned abrasive materials, suspended in a water-based liquid.In contrast to the Si and oxide-type polishing slurries, the pH may beacidic (i.e., <5) or neutral and is obtained and controlled by additionof acid(s) or salt(s) thereof. In addition to the organic acid(s) orsalt(s), metals polishing slurries include one or more oxidizing agentsfor assisting in metal dissolution and removal, typically selected fromhydrogen peroxide, potassium ferricyanide, ferric nitrate, orcombinations thereof.

[0008] However, the combination of acidic or neutral pH and presence ofoxidizing agent(s), hereafter “oxidizer(s)”, in CMP metals polishingslurries can result in several disadvantages, drawbacks, anddifficulties, including, inter alla:

[0009] (a) the oxidizer can continue to etch the electrically conductivematerial, e.g., metal, during “static” periods, i.e., periods whenmechanical polishing is not being performed but the substrate surfaceremains in contact with the polishing slurry containing at least oneoxidizer, e.g., upon completion of CMP but prior to removal of thesubstrate surface from contact with the slurry. As a consequence,unwanted static etching of the metallic features of the polished surfacecan occur, disadvantageously resulting in formation of depressionstherein, referred to as “dishing”, which phenomenon remains asignificant problem in metal CMP processes;

[0010] (b) the amount of oxidizer present in the metals polish slurriesis not constant during the interval necessary for completion of the CMPprocessing, but rather varies during the course of CMP as a result ofconsumption thereof during the metal oxidation process. As aconsequence, the concentration of oxidizer in the slurry, hence the rateof metal oxidation, is not controlled throughout processing, unlesscontinuous, reliable detection/concentration measurement andreplenishment means are provided, which means undesirably add to thecost of CMP processing;

[0011] (c) in some instances, the presence of oxidizer in the metalspolishing slurry is particularly undesirable during a specific portionof the CMP processing. For example, the presence of oxidizer in theslurry during the later stage(s) of polishing frequently results in theabove-mentioned problem of “dishing”, i.e., a height differentialbetween a dielectric oxide layer and metallization features within anarray of metallization features, as well as undesirable corrosion and“erosion”, i.e., a height differential between a dielectric oxide layerin an open field region and in an array of metallization features; and

[0012] (d) the presence of oxidizer(s) and spent oxidizer(s), e.g.,peroxide, Fe ions, etc., in spent (i.e., waste) abrasive slurry adds tothe complexity, problems, and expense associated with handling anddisposal of the waste slurry in an environmentally acceptable manner.

[0013] U.S. Pat. No. 4,839,005 discloses a method and apparatus forproviding mirror-smooth finishes to aluminum surfaces by applying aconstant anodic potential to the surface via a passivation-typeelectrolyte solution, while simultaneously performing mechanicalpolishing thereof with an abrasive slurry or cloth. While suchelectrolytically-assisted polishing may dispense with the requirementfor a chemical oxidizer in the polishing slurry or abrasive cloth, theapplication of a constant anodic potential renders the disclosedmethod/apparatus unsatisfactory for use in the planarization ofworkpieces comprising semiconductor wafers with surfaces havingelectrically conductive wirings, etc., in that undesirable dishing wouldstill occur during the late stage(s) of planarization due to excessive,electrochemically promoted anodic metal dissolution, as in theconventional methodology employing chemical oxidizing agent(s).

[0014] Accordingly, there exists a need for a simplified and reliablemethod and apparatus for performing planarization processing,particularly of semiconductor wafer substrates comprising surfacesincluding metallization patterns on or within a dielectric materiallayer, which method and apparatus are free of the disadvantages anddrawbacks associated with the conventional CMP methodologies, and arefully compatible with the economic and product throughput requirementsof automated semiconductor manufacture processing.

[0015] The present invention addresses and solves the above-describedproblems attendant upon the manufacture of integrated circuitsemiconductor and other electrical and electronic devices according toconventional CMP methodology utilizing abrasive slurries containingchemical oxidizer agent(s), and is fully compatible with all othermechanical aspects of CMP-type planarization processing.

DISCLOSURE OF THE INVENTION

[0016] An aspect of the present invention is an improved method ofplanarizing workpiece surfaces comprising an electrically conductivematerial.

[0017] Another aspect of the present invention is an improved method ofplanarizing a workpiece surface by means of anelectrochemical-mechanical planarization (EMP) process and apparatusutilizing an abrasive slurry free of chemical oxidizing agent(s).

[0018] Yet another aspect of the present invention is an improved methodof controllably planarizing a workpiece surface.

[0019] Still another aspect of the present invention is an improvedmethod of controllably planarizing a semiconductor substrate surfacecomprising a pattern of electrical conductors.

[0020] A still further aspect of the present invention is improvedapparatus for controllably performing EMP of at least one surface of atleast one workpiece.

[0021] A yet another aspect of the present invention is improvedapparatus for performing EMP of a workpiece surface with anoxidizer-free abrasive slurry.

[0022] Additional aspects and other features of the present inventionwill be set forth in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from the practice of thepresent invention. The advantages of the present invention may berealized and obtained as particularly pointed out in the appendedclaims.

[0023] According to one aspect of the present invention, the foregoingand other advantages are achieved in part by a method of planarizing asurface of a workpiece by electrochemical-mechanical planarization(EMP), which method comprises the steps of:

[0024] (a) providing a chemical-mechanical polishing (CMP) apparatuswith at least one workpiece having at least one surface to be planarizedby EMP;

[0025] (b) supplying the CMP apparatus with an electrolyticallyconductive fluid free of chemical oxidizing agent(s); and

[0026] (c) planarizing the at least one workpiece surface by EMPutilizing the CMP apparatus, the planarizing by EMP including applying atime-varying electrochemical potential to the at least one workpiecesurface.

[0027] In embodiments according to the present invention, step (c)comprises performing EMP by controllably applying a time-varying anodicpotential to the at least one workpiece surface. In particularembodiments according to the present invention, step (c) comprisesapplying a first, higher anodic potential during an initial stage of theEMP and applying a second, lower anodic potential at or during a laterstage of the EMP; or step (c) comprises reducing the first, higheranodic potential to the second, lower anodic potential during anintermediate stage of the EMP, e.g., continuously reducing the anodicpotential during the intermediate stage; or step (c) comprises rapidlyreducing the anodic potential from the first, higher potential to thesecond, lower potential after a predetermined interval at the first,higher potential.

[0028] According to further embodiments of the present invention, step(c) comprises applying the time-varying electrochemical potential from acontrollably variable DC power supply, e.g., an electronic potentiostat;and a further step (d) comprises monitoring the extent of the EMP of theat least one workpiece surface in order to determine the end-pointthereof. According to particular embodiments of the present invention,step (d) comprises coulometrically monitoring the extent of EMP, or step(d) comprises monitoring a signal from a sensor utilized for measuring aphysical property (e.g., electrical resistance or conductance)) oroptical property (e.g., reflectance) of the at least one workpiecesurface.

[0029] According to yet further embodiments of the present invention,step (a) comprises providing a semiconductor wafer substrate as theworkpiece, the semiconductor wafer substrate comprising the at least oneworkpiece surface and including a pattern of electrical conductorsformed on or within a layer of a dielectric material; and step (b)comprises supplying the CMP apparatus with an oxidizer-free,electrolytically conductive, abrasive slurry comprisingfinely-dimensioned abrasive particles and at least one pH adjustingagent.

[0030] According to still further embodiments according to the presentinvention, step (a) comprises providing a CMP apparatus having anon-abrasive polishing pad and step (b) comprises supplying the CMPapparatus with an oxidizer-free, electrolytically conductive fluidcomprising an abrasive slurry comprising finely-dimensioned abrasiveparticles; or step (a) comprises providing a CMP apparatus having anabrasive polishing pad and step (b) comprises supplying the CMPapparatus with an oxidizer-free, electrolytically conductive fluidcomprising a non-abrasive liquid; or step (a) comprises providing a CMPapparatus having a non-abrasive polishing pad and step (b) comprisessupplying the CMP apparatus with an oxidizer-free, electrolyticallyconductive fluid comprising a non-abrasive liquid.

[0031] According to another aspect of the present invention, apparatusfor performing electrochemical-mechanical planarization (EMP) of atleast one surface of at least one workpiece comprise: (a) a deviceadapted for performing chemical-mechanical polishing (CMP) of the atleast one workpiece surface; and (b) a power supply connected to theCMP-adapted device for providing a controllable, time-varying DCelectrochemical potential to the at least one workpiece surface foreffecting EMP thereof.

[0032] In embodiments according to the present invention, the device (a)adapted for performing CMP of at least one workpiece surface comprisesan abrasive polishing pad or a non-abrasive polishing pad; power supply(b) comprises an electronic potentiostat adapted for applying atime-varying, anodic electrochemical potential to the at least oneworkpiece surface; and the apparatus further comprises a device (c) formonitoring the extent of EMP of the at least one workpiece surface fordetermining the end-point thereof. According to particular embodimentsof the present invention, the monitoring device (c) comprises acoulometer or a sensor for providing a signal indicative of a physical(e.g., electrical) or optical property of the at least one workpiecesurface.

[0033] Additional advantages of the present invention will becomereadily apparent to those skilled in the art from the following detaileddescription, wherein only the preferred embodiment of the presentinvention is shown and described, simply by way of illustration of thebest mode contemplated for carrying out the method of the presentinvention. As will be described, the present invention is capable ofother and different embodiments, and its several details are capable ofmodification in various obvious respects, all without departing from thepresent invention. Accordingly, the drawing and description are to beregarded as illustrative in nature, and not as limitative.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The following detailed description of the embodiment of thepresent invention can best be understood when read in conjunction withthe following drawings, wherein:

[0035]FIG. 1 is a graph illustrating several examples of anodicpotential vs. time profiles usable according to the practice of thepresent invention;

[0036]FIG. 2 illustrates, in simplified cross-sectional schematic form,an embodiment of an electrochemical-mechanical planarization (EMP)apparatus according to the present invention;

[0037]FIG. 3 illustrates, in simplified cross-sectional schematic form,another embodiment of another EMP apparatus according to the presentinvention;

[0038]FIG. 4 illustrates, in exploded perspective view, yet anotherembodiment of an EMP apparatus according to the present invention;

[0039]FIG. 5 illustrates, in simplified cross-sectional schematic form,a portion of the EMP apparatus of FIG. 4; and

[0040]FIG. 6 illustrates, in simplified form, a plan view of a retainingring of the EMP apparatus of FIG. 4.

DESCRIPTION OF THE INVENTION

[0041] The present invention is based upon the discovery thatelectrochemical-mechanical planarization (EMP) processing of workpiecesurfaces, e.g., semiconductor wafer substrates having electricallyconductive patterns formed therein or thereon, such as are utilized inintegrated semiconductor device manufacture, can be performed inchemical-mechanical polishing apparatus having abrasive or non-abrasivepolishing pads and appropriately modified to apply a time-varyingelectrochemical potential to the workpiece surface, i.e., an anodicpotential, and wherein oxidizer-free fluids such as abrasive slurries ornon-abrasive liquids are utilized, thereby, inter alia, advantageouslyeliminating problems of dishing and corrosion as are commonlyencountered during static periods and in the later stages ofconventional CMP planarization processing.

[0042] Briefly stated, according to the present invention, instead ofeffecting metals dissolution/removal by means of chemical oxidizeragent(s), an anodic electrochemical potential is applied to the surfacebeing polished, which surface includes a pattern of metal conductors,and the abrasive slurry or non-abrasive liquid supplied to the apparatusis free of chemical oxidizer(s). The applied anodic electrochemicalpotential is advantageously controlled by means of a programmableelectronic potentiostat, whereby potential control is easy and precise.During the initial stage(s) of the polish, a relatively high anodicpotential is applied to the metal-bearing workpiece surface to promoterelatively aggressive (i.e., high rate) oxidation/dissolution/removal ofthe metal pattern. When polishing is at a later stage, e.g., whenapproaching an underlying barrier layer, such as of tantalum (Ta), theapplied anodic potential is reduced to a level producing substantiallyless aggressive (i.e., low or negligibly low rate)oxidation/dissolution/removal of the metal features, thereby eliminatingor substantially reducing static etching and resultant dishing,corrosion, and erosion as encountered with conventional CMP processing.

[0043] According to the present invention, the application of atime-varying anodic electrochemical potential to the workpiece surfacefor assisting in metals dissolution/removal, i.e., as a replacement forthe chemical oxidizer agent(s) present in conventional CMP metalspolishing slurries, entails a number of advantages vis-à-vis the latter,including the following:

[0044] a. the concentration of chemical oxidizers in metals polishingslurries utilized in conventional CMP planarization processing, hencethe rate of metals oxidation/dissolution, is not easily controlledduring polishing, whereas, according to the present invention, the levelof the anodic electrochemical potential applied to the workpiecesurface, which level determines the rate of metalsoxidation/dissolution, is readily adjustable and controllable with greatprecision;

[0045] b. in conventional metals polishing/planarization by CMP, thepresence of chemical oxidizer(s) during the late stages of polishingcauses problems of dishing, corrosion, and erosion, particularly duringstatic periods after completion of polishing but prior to removal of theworkpiece surface from contact with the abrasive slurry. However,according to an advantageous feature of the present invention, theapplied anodic potential during the later stage(s) of thepolishing/planarization processing can be reduced to a desired low levelwhereat metals dissolution occurs only at a negligibly low rate, therebyeliminating problems of dishing, corrosion, and erosion;

[0046] c. in conventional metals polishing/planarization by CMP, therate of polishing/planarization is strongly dependent upon chemical andkinetic factors, e.g., the particular oxidizer species and concentrationthereof, temperature, diffusion of reactants and products, etc.,whereas, according to the present invention employing EMP methods andapparatus, workpiece throughput can be significantly increased over thatobtainable by conventional CMP techniques by application of high levelsof anodic electrochemical potential during the early stage(s) ofpolishing, whereby aggressive metals dissolution/removal rates can beobtained;

[0047] d. inasmuch as the cost of the necessary electrical currentaccording to the present invention is substantially lower than that ofequivalent quantities of chemical oxidizer(s), EMP processing iseconomically favorable vis-à-vis conventional CMP processing; and

[0048] e. the absence of oxidizing agents (e.g., peroxides, cyanides, Feions) in spent slurry or non-abrasive liquid simplifies waste handlingaccording to environmentally acceptable standards.

[0049] Referring now to FIG. 1, illustrated therein, by way ofillustration but not limitation, are several examples of applied anodicpotential vs. time profiles suitable for use in the present invention.However, given the present disclosure and objectives of the presentinvention, it is considered within the scope of ordinary variation todetermine other profiles for use in a given application. Further, whilethe illustrated and other possible anodic voltage vs. time profiles arebest obtained by means of a conventional 3-electrode (i.e., working,reference, and counter electrodes), programmable electronic potentiostatsystem, a programmable 2-electrode (i.e., working and counterelectrodes) power supply may be employed where less precise control ofthe applied anodic potential is satisfactory.

[0050] Curve A of FIG. 1 illustrates a case where a relatively high,constant anodic potential is first applied to the workpiece surface fora specific interval during the initial polishing stage in order topromote aggressive, i.e., high rate, metal oxidation/dissolution/removalas to reduce overall processing time and increase product throughput,followed by a linear decrease in applied anodic potential during anintermediate polishing stage to a preselected relatively low anodicpotential providing a low or negligible metals dissolution rate,followed in turn by maintenance of the relatively low anodic potentialduring the final polishing stage.

[0051] By contrast, curve B of FIG. 1 illustrates a case where theinitial, relatively high, anodic potential applied at the initialpolishing phase is continuously reduced during the entire polishinginterval to the relatively low level achieved during the final polishingstage. Curve C of FIG. 1 illustrates yet another case where the initial,relatively high anodic potential is maintained constant for apredetermined interval and then rapidly reduced to the relatively lowlevel for the remainder of the polishing process.

[0052] As should be readily apparent, a large number and variety ofapplied anodic potential vs. time profiles are usable within the contextand spirit of the present invention. Moreover, the specific voltagelevels, intervals, rates of decrease, etc., are readily optimized by oneof ordinary skill for use in a particular application, e.g., dependingupon the particular metal(s) to be polished/planarized and thethicknesses thereof.

[0053]FIG. 2 schematically illustrates, in simplified cross-sectionalform, an embodiment of an apparatus according to the present invention,comprising a CMP-type apparatus modified to perform EMP processing. Asillustrated, apparatus 20 comprises a rotational driving mechanism 1 forrotating shaft 1 a, which shaft in turn rotates tool electrode 2 formedof an electrochemically inert metal or metal alloy. Tool electrode 2 isdisc-shaped and mounts on the lower surface thereof a liquid-permeable,non-conductive, polishing pad 3. Rotational driving mechanism 1 isadapted to provide a predetermined downwardly urging pressure of thepolishing pad 3 during rotation. An abrasive slurry/liquid electrolytesupply 2 a conduit is formed within the central elongated portion oftool electrode 2 and the center of polishing pad 3 and includes aplurality of radially extending channels formed within the lower padsurface for evenly supplying the liquid-permeable polishing pad 3 andthe space therebelow with slurry/electrolyte. Tool electrode 2 iselectrically connected to the counter-electrode terminal C ofprogrammable electronic potentiostat 5 and typically is negatively(i.e., cathodically) biased during polishing/planarization processing.

[0054] Movable table 4a mounting a workpiece 6 on its upper surface infacing relation to the lower surface of polishing pad 3 is disposedbelow the tool electrode 2, and is reciprocated by means of feed motor 4b and associated mechanism, leftwardly and rightwardly as shown in thefigure. At least the upper surface of workpiece 6 comprising a patternof electrical, e.g., metal, conductors therein or thereon iselectrically connected to the working electrode terminal W ofpotentiostat 5 and typically is positively (i.e., anodically) biasedduring polishing/planarization processing. A reference electrode 7,typically formed of an inert metal, e.g., platinum (Pt), or of Ag/AgCl,is electrically connected to the reference electrode terminal R ofpotentiostat 5 and extends through the slurry/electrolyte supply conduit2 a of tool electrode 2, whereby the exposed tip thereof is positionedin close proximity to the upper surface of workpiece 6.

[0055] A slurry/electrolyte supply conduit 8 is connected to aslurry/electrolyte supply vessel or reservoir 9 for supplying anoxidizer-free, abrasive particle-containing, slurry/electrolyte betweenthe polishing pad 3 and the upper surface of workpiece 6. A supply pump8 a, flow meter 8 b, and pressure gage 8 c are disposed between supplyconduit 8 and supply vessel 9. The slurry/electrolyte is supplied fromthe supply vessel 9 by way of the supply conduit 8 and fed through theslurry/electrolyte supply conduit 2 a to be between the polishing pad 3and the upper surface of workpiece 6, and is returned to supply vessel 9by way of return conduit 10. A slurry/liquid waste processing device 11is optionally provided for disposal of spent slurry/electrolyte afterexcessive accumulation therein of dissolved metal(s) from workpiece 6.

[0056] Electronic potentiostat 5 is provided with internal or externalprogramming means (not shown for illustrative simplicity), as areconventional in the art, for supplying any of a variety of desiredanodic potential vs. time profiles to workpiece 6. As previouslyindicated, a programmable 2-electrode DC power supply can be utilized inthe event less precise control of the applied anodic voltage isacceptable. Moreover, a coulometer 12 can be provided in either theworking or counter-electrode supply lines for determining an end-pointof EMP processing, e.g., when a predetermined amount of current flowindicating a predetermined amount of metal dissolution, has occurred.Alternatively, a sensor 13, positioned adjacent the upper, polishedsurface of workpiece 6 and operatively connected to a measuring device14 may be utilized for determining an end-point of EMP by measuringand/or detecting a change in a physical (e.g., electrical) or opticalproperty thereof.

[0057]FIG. 3 schematically illustrates, in simplified cross-sectionalform, another embodiment of an EMP apparatus according to the presentinvention. Apparatus 40 resembles known apparatus for performing CMP ofworkpiece substrates such as semiconductor wafers, and comprises, inpertinent part, a workpiece holder 21 connected at its underside toshaft 22 for rotation of a workpiece 23 (e.g., a semiconductor waferhaving at least one electrical, i.e., metal, conductor formed in or onthe upwardly facing surface 23′ thereof) about a central axis 24, whileurging the upwardly facing workpiece surface 23′ with force F₁ againstthe downwardly facing surface 25′ of porous electrolyteapplicator/polishing pad. Electrolyte applicator/polishing pad 25 isadapted (by means not shown for illustrative simplicity) for rotatingabout a central axis 26 in a direction counter to that of workpieceholder 21 while urging downwardly facing surface 25′ with force F₂against upwardly facing workpiece surface 23′. Apparatus 40 furtherincludes a programmable electronic potentiostat 27, of conventionaltype, the working electrode terminal W (typically of positive polarity)being operatively connected by line 28 to rotatable shaft 22 forestablishing anodic electrochemical conditions at workpiece surface 23′.The counter-electrode terminal C (typically of negative polarity) ofelectronic potentiostat 27 is operatively connected by line 29 toelectrochemically inert counter-electrode 30 located on the upwardlyfacing surface 25″ of electrolyte applicator/polishing pad 25, forestablishing cathodic electrochemical conditions at the downwardlyfacing surface 30′ thereof. In the illustrated embodiment, the tip of areference electrode 34, typically of an inert metal, e.g., Pt, ispositioned in close proximity to the workpiece surface 23′ in thenarrow, electrolyte-filled space between the lower surface 25′ of theapplicator/polishing pad 25 and the workpiece upper surface 23′ and isoperatively connected to the reference electrode terminal R ofpotentiostat 27 via line 35. However, it is within the ambit of thepresent invention to provide other physically configured arrangementsfor positioning the tip of the reference electrode in electrolyte inclose proximity to the workpiece upper surface 23′. A spray of anoxidizer-free slurry/electrolyte 31 comprising abrasive particles ofsufficiently small dimension as to pass freely through the porouselectrolyte applicator/polishing pad 25 is supplied to the upwardlyfacing surface 25″ of the pad from slurry/electrolyte reservoir 32 bymeans of supply conduit 33, for replenishing consumed slurry/electrolyte31 and maintaining the pores of the electrolyte applicator/polishing 25pad in a filled state.

[0058] As in the embodiment illustrated in FIG. 2, the embodiment ofFIG. 3 may employ a 2-electrode programmable DC power supply ifdiminished precision of anodic potential control is acceptable in aparticular situation, thereby dispensing with the need for referenceelectrode 34 and its associated positioning means. In addition, acoulometer may be electrically positioned in either the workingelectrode or counter-electrode circuit for providing end-pointindication, as in the earlier embodiment. Finally, a sensor andmeasuring means for determining a physical (e.g., electrical) or opticalproperty of the polished surface for determining the end-point of EMPprocessing may also be provided, as in the earlier embodiment.

[0059] Referring now to FIGS. 4-6, illustrated therein is yet anotherembodiment of an EMP apparatus according to the present invention, whichapparatus is a of a multi-station type such as is employed in automatedsemiconductor manufacture. With particular reference to FIG. 1,illustrated therein in schematic, exploded view, is a multi-station CMPapparatus 50 including a lower machine base 51 having an upper tablesurface 52 and a removable upper cover (not shown). As shown, uppertable surface 52 supports thereon a plurality of chemical-mechanicalpolishing stations 53 a, 53 b, and 53 c and a transfer station 54 whichserves for providing a plurality of functions, including, inter alia,receiving substrates from a loading apparatus (not shown forillustrative simplicity), washing the substrates, loading the substratesonto carrier heads, receiving polished substrates, and transferring thepolished substrates back to the loading apparatus.

[0060] Each polishing station 53 a, 53 b, and 53 c includes a rotatableplaten 55 on which is mounted a polishing pad 56 and each of thepolishing stations may further include an associated pad conditionerapparatus 57 for maintaining the condition of the respective polishingpad so that it will effectively polish a substrate pressed against itwhile rotating. Intermediate washing stations 58 are positioned betweenneighboring polishing stations 53 a, 53 b, 53 c and transfer station 54for rinsing substrates as they pass from one polishing station toanother.

[0061] Positioned above the lower machine base 51 is a rotatablemulti-head carousel 59, supported by a center post 60 located on theupper table surface 52 and adapted for rotation about carousel axis 61by means of a motor located within base 51. The center post 60 supportsa carousel base plate 62 and associated cover 63. The multi-headcarousel 59 includes a plurality of head systems 64, illustrativelyfour, i.e., 64 a, 64 b, 64 c, and 64 d. Three of the carrier headsystems mount thereon a substrate, and polish the respective surfacethereof by pressing it against an opposing polishing pad 56 mounted onthe platen 55 of polishing stations 53 a, 53 b, and 53 c. One of thecarrier head systems receives substrates from, and delivers substratesto, transfer station 54.

[0062] Typically, the four carrier head systems 64 a-64 d are mounted onthe carousel base plate 62 at equidistant intervals about the carouselrotational axis 61. Center post 60 supports carousel base plate 62 andallows the carousel motor to rotate the carousel base plate 62 and toorbit the carrier head systems 64 a-64 d, and the substrates mountedthereon, about carousel axis 61. Each of the carrier head systems 64a-64 d includes a polishing or carrier head (shown in more detail inFIG. 5), which carrier rotates about its own rotational axis via arespective motor 65 coupled to drive shaft 66, and independentlylaterally oscillates in a radially extending slot 67 formed in thecarousel base plate 62.

[0063]FIG. 5 illustrates, in schematic, cross-sectional view, one of thecarrier head systems 64 a-64 d in operative position facing a polishingpad 56 of a polishing station 53 for polishing/planarization of a wafersubstrate 68, which carrier head system is adapted for performingelectrochemical-mechanical planarization (EMP) according to the presentinvention. As shown therein, rotatable drive shaft or spindle 66 isoperatively connected to rotating polishing head assembly 69 comprisinga circularly-shaped, inner mounting piece 70 having a narrow, shaft-likeaxially extending upper portion 71 connected to drive shaft 66 and awide lower portion 72 having a non-conductive membrane 73 on its lowersurface for mounting wafer substrate thereon, and an outer,annularly-shaped mounting piece 74 having an inwardly extending flangeportion 75 at its upper end and an annularly-shaped retaining ring 76 atits lower end.

[0064] According to the present invention, the CMP apparatus 50, asdescribed supra, is modified, as in the previous embodiments, to providefor controlled application of a time-varying electrochemical potential,e.g., a variable anodic potential, to wafer substrate 68 for performingEMP processing. Accordingly, programmable electronic potentiostat 77having working (w), counter (c), and reference (r) electrode outputs isoperatively connected to the polishing head assembly 69 by means ofrespective electrical leads 78, brush-type electrical contactors 79, andconcentric contact rings 80 formed on the upper surface of the widelower portion 72 of mounting piece 70. Respective electrical leadsconnected to contact rings 80 are connected to an annularly-shapedelectrical contact located between insulative membrane 73 and the rearsurface of wafer substrate 68, inwardly of the wafer circumference, forpermitting functioning of the wafer as a working (w) electrode, and toan alternating plurality of counter electrodes 81 (e.g., of anelectrochemically inert, electrically conductive material such as Pt orC) and reference electrodes 82 (e.g., of Pt or Ag/AgCl) positioned ingrooved recesses 83 formed in the lower surface of retaining ring 76, asshown in greater detail in FIG. 6.

[0065] As in the previous embodiments, the reference electrodes 82 maybe dispensed with, if desired, and a 2-electrode programmable DC powersupply utilized in place of the 3-electrode potentiostat 77 of theillustrated embodiment, provided reduced precision of control of anodicpotential applied to the wafer substrate 68 is acceptable in aparticular situation. Moreover, as before, a coulometer may beelectrically positioned in either the working electrode orcounter-electrode circuit for providing end-point indication/detection.Alternatively, a sensor and measuring means for determining a physicalproperty (e.g., electrical resistance as determined by a conventional4-contact probe device) or an optical property of the polished surface(e.g., reflectance as indicated by means of a conventional lightsource/photocell apparatus) for determining the end-point of EMPprocessing may also be provided, as in the previously describedembodiments.

[0066] A number of advantages are thus provided by the presentinvention, including, but not limited to, substantial reduction orelimination of undesirable dishing and erosion in planarization ofsemiconductor wafer surfaces comprising electrically conductivepatterns, elimination of chemical oxidizers from waste slurry streams,reduced cost, improved control of planarization, and increasedmanufacturing throughput for economic competitiveness. Moreover, thepresent invention is advantageously fully compatible with all aspects ofconventional process technology, e.g., CMP processing of semiconductorwafers utilized in integrated circuit semiconductor device manufacture.In addition, the inventive concept disclosed herein may be applied toCMP processing and apparatus therefor which do not employ abrasiveslurries, e.g., where an abrasive or non-abrasive polishing/planarizingpad is employed in combination with an electrolytically conductive,non-abrasive particle-containing liquid.

[0067] In the previous descriptions, numerous specific details are setforth, such as particular materials, structures, reactants, processes,etc., in order to provide a thorough understanding of the presentinvention. However, it should be recognized that the present inventioncan be practiced without resorting to the details specifically setforth. For example, the present invention is applicable to planarizationof a variety of substrates, including, but not limited to semiconductorwafers and electronic circuit board manufacture. In other instances,well-known processing structures and techniques have not been describedin detail in order not to unnecessarily obscure the present invention.

[0068] Only the preferred embodiments of the present invention are shownand described herein. It is to be understood that the present inventionis capable of changes and/or modifications within the scope of theinventive concept as expressed herein.

What is claimed is:
 1. A method of planarizing a surface of a workpieceby electrochemical-mechanical planarization (EMP), comprising the stepsof: (a) providing a chemical-mechanical polishing (CMP) apparatus withat least one workpiece having at least one surface to be planarized byEMP; (b) supplying said CMP apparatus with an electrolyticallyconductive fluid free of chemical oxidizing agent(s); and (c)planarizing the at least one workpiece surface by EMP utilizing said CMPapparatus, said planarizing by EMP including applying a time-varyingelectrochemical potential to the at least one workpiece surface.
 2. Themethod according to claim 1, wherein: step (c) comprises performing saidEMP by controllably applying a time varying anodic potential to said atleast one workpiece surface.
 3. The method according to claim 2,wherein: step (c) comprises applying a first, higher anodic potential tosaid workpiece surface during an initial stage of said EMP and applyinga second, lower anodic potential to said workpiece surface at or duringa later stage of said EMP.
 4. The method according to claim 3, wherein:step (c) comprises reducing said first, higher anodic potential to saidsecond, lower anodic potential during an intermediate stage of said EMP.5. The method according to claim 4, wherein: step (c) comprisescontinuously reducing said anodic potential during said intermediatestage.
 6. The method according to claim 3, wherein: step (c) comprisesrapidly reducing said anodic potential from said first, higher potentialto said second, lower potential.
 7. The method according to claim 1,wherein: step (c) comprises applying said time-varying electrochemicalpotential from a controllably variable DC power supply.
 8. The methodaccording to claim 7, wherein: step (c) comprises utilizing aprogrammable electronic potentiostat.
 9. The method according to claim1, further comprising the step of: (d) monitoring the extent of said EMPof said at least one workpiece surface in order to determine theend-point thereof.
 10. The method according to claim 9, wherein: step(d) comprises coulometrically monitoring the extent of EMP.
 11. Themethod according to claim 9, wherein: step (d) comprises monitoring asignal from a sensor utilized for measuring a physical or opticalproperty of said at least one workpiece surface.
 12. The methodaccording to claim 1, wherein: step (a) comprises providing asemiconductor wafer substrate as said at least one workpiece, saidsemiconductor substrate comprising said at least one workpiece surfaceand including a pattern of electrical conductors formed on or within alayer of a dielectric material.
 13. The method according to claim 1,wherein: step (a) comprises providing a CMP apparatus having anon-abrasive polishing pad; and step (b) comprises supplying the CMPapparatus with an oxidizer-free, electrolytically conductive fluidcomprising an abrasive slurry comprising finely-dimensioned abrasiveparticles.
 14. The method according to claim 1, wherein: step (a)comprises providing a CMP apparatus having an abrasive polishing pad;and step (b) comprises supplying the CMP apparatus with anoxidizer-free, electrolytically conductive fluid comprising anon-abrasive liquid.
 15. The method according to claim 1, wherein: step(a) comprises providing a CMP apparatus having a non-abrasive polishingpad; and step (b) comprises supplying the CMP apparatus with anoxidizer-free, electrolytically conductive fluid comprising anon-abrasive liquid.
 16. An apparatus for performingelectrochemical-mechanical planarization (EMP) of at least one surfaceof at least one workpiece, comprising: (a) a device adapted forperforming chemical-mechanical polishing (CMP) of said at least oneworkpiece surface; and (b) a power supply connected to the CMP apparatusfor providing a controllable, time-varying DC electrochemical potentialto the at least one workpiece surface for effecting EMP thereof.
 17. Anapparatus as in claim 16, wherein: said power supply (b) comprises anelectronic potentiostat adapted for applying a time-varying anodicelectrochemical potential to said at least one workpiece surface.
 18. Anapparatus as in claim 16, further comprising: (c) a device formonitoring the extent of said EMP of said at least one workpiece surfacefor determining the end-point thereof.
 19. An apparatus as in claim 18,wherein: said monitoring device (c) comprises a coulometer.
 20. Anapparatus as in claim 18, wherein: said monitoring device (c) comprisesa sensor for providing a signal indicative of a physical or opticalproperty of said at least one workpiece surface.